Study on the Percolation Characteristics of Oil-Water Two-phase Flow in Extra-low Permeability Reservoirs

摘要

The variable and micro effects of pore size make fluid flow more complex in extra low permeability reservoirs, which cause non-linear fluid flow and starting pressure gradient. In this paper, the laboratory experiments were conducted upon the natural extra-low permeability cores at different permeability levels gotten from Yanchang oilfield. The starting pressure gradients of single phase and oil-water two-phase flow under different water saturation conditions were measured by capillary pressure equilibrium method. The results show that the starting pressure gradient decreases while the displacement fluid mobility increases, but it decreases gradually and smoothly when the mobility reaches a special value. The minimum starting pressure gradient of oil and water two-phase is a power exponential function of mobility, and it increases at first and then decreases with the increase of water saturation. In addition, the starting pressure gradient of two-phase flow is higher than that of single phase flow. The relative permeability curves of extra low permeability reservoir are characterized by high irreducible water saturation, high remaining oil saturation and the oil-phase curve decreases fast, while the water-phase curve increases slowly, which is in straight line or bow-shape in common. At the end, some suggestions to improve the development are provided based on the research.